Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $44.60   6.136%   $47.3367   $47.34   $47.35   $47.30  
  Purchase #2 $34.55   9.488%   $37.8281   $37.83   $37.85   $37.80  
  Purchase #3 $166.38   11.511%   $185.532   $185.53   $185.55   $185.50  
  Purchase #4 $220.58   5.226%   $232.1075   $232.11   $232.10   $232.10  
  Purchase #5 $234.52   13.441%   $266.0418   $266.04   $266.05   $266.00  
  Purchase #6 $58.38   8.870%   $63.5583   $63.56   $63.55   $63.60  
  Purchase #7 $212.97   5.704%   $225.1178   $225.12   $225.10   $225.10  
  7 purchase totals = $971.98       $1,057.5222   $1,057.53   $1,057.55   $1,057.40